Visual contrast thresholds for moving point sources:

Over a wide range of brightness of the adapting field, for different color combinations of stimulus and adapting field, contrast thresholds for moving point sources are measured, as a function of the length of the covered track, for different exposure times. When the brightness B of the adapting field does not exceed certain limits, the experimental results agree with the quantum theory of vision, when the known behavior of the summative properties of the retina is taken into account. For backgrounds with high brightness level, deviations from this description occur. These deviations are probably due to increasing saturation of the activated nerve fibers and decrease of the concentration of rhodopsin with increasing brightness of the adapting field. The importance of these effects differs for stimuli of various lengths and exposure times.